1. Field of the Invention
The present invention relates generally to drill bits for boring an earth formation and more particularly to such bits which include structures for breaking formation chips during drilling.
2. Description of the Related Art
Drilling in shale or plastic formations, or in hard formations which act in a plastic manner, with a drill bit has always been difficult. The shale, under pressure and in contact with hydraulics, tends to act like a sticky mass, sometimes referred to as gumbo, which balls and clogs the bit. Once the bit balls up, it ceases to cut effectively.
One type of bit includes polycrystalline diamond compact (PDC) cutters which present a generally planar cutting face having a generally circular perimeter. A cutting edge is formed on one side of the cutting face which, during boring, is at least partially embedded into the formation so that the formation is received against at least a portion of the cutting surface. As the bit rotates, the cutting face moves against the formation and a chip, which rides up the surface of the face, forms. When the bit is functioning properly, the chip breaks off from the remainder of the formation. Drilling fluid, which is typically pumped down a drill string to which the bit is attached, flows through openings formed in the bit and into courses which are typically formed on the operating face of the bit adjacent the cutters. Fluid flowing through the courses breaks off chips formed by the cutters and transports the cuttings upwardly out of the bore hole. Additional chips are continuously formed, each one sliding up the face of the cutting surface and breaking off in a similar fashion. Such action occurring at each cutting element on the bit causes the bore to become progressively deeper.
As mentioned above, in some formations the chip formed at the cutter is not easily broken from the formation. In prior art bits, the chip, which is of substantially planar configuration, is typically parallel to the face of the cutter. The fluid course typically comprises a shallow trough which directs fluid across the face of the bit also parallel to the cutting face of each cutter. A relatively small surface area of each chip, namely the edge, is therefore presented to the fluid flow in the course. It would be desirable to present a larger surface area of the chip to the fluid flow thereby increasing the total force exerted by the fluid against each chip and increasing the likelihood that the chip will break off from the formation. It would also be desirable to impart strain to the chip in order to increase the likelihood that it will break from the formation.